A substantial portion of the total amount of energy consumed annually is used for heating and cooling of buildings, including homes, factories, office buildings and the like. As a result of the tremendous increases in energy costs, it has become cost effective on a long term basis to invest larger sums of money in energy conservation than it was in the past when energy was relatively inexpensive. Architects and engineers have become aware of this fact, and previously unused or little used technology for the more efficient use of natural energy resources, such as active or passive solar heating and the increased use of old technology such as building insulation, can be economically incorporated in virtually any building when the long range cost savings therefrom are considered. Solar collectors to harness the energy from the sun have been developed and altered, made complicated and simplified, with predictably mixed results, particularly in severe climates and in areas which experience extended periods of cloudiness or overcast skies. One of the principal difficulties with the use of previous solar energy systems for heating buildings is that, in addition to the large initial installation cost, the systems generally require direct, intense sunlight. The rays from the sun are most indirect, and thus most inefficient, during the coldest months of the year when heating is required in a building, and the rays are most direct, and hence most heat creative for a solar heating system, during the summer months when typically the requirement is for cooling a building. Previous solar systems do not work well during cloudy or overcast days, and without storage systems, may cease operating entirely if prolonged absences of direct sunlight occur.
The largest and most reliable solar energy collector available to mankind is the earth itself. It has long been known that subsurface ground temperatures below the frost line are relatively stable. At a depth of 10 to 12 feet below the ground surface in most temperate zone locations, a relatively constant ground temperature of 55.degree. is present. Heating and cooling of the ground at more shallow depths do occur; however, the rate at which temperatures at the surface of the ground penetrate into the ground in slow. Hence, the highest subsurface soil temperatures are reached during the late fall and early winter months when above ground temperatures approach the coldest, and the coolest subsurface temperatures are present during the late spring and early summer months when the above surface temperatures are approaching the warmest. This phenomenon, whereby the subsurface temperature cycle is out of phase with the above ground temperature cycle, is referred to as a "thermal fly wheel" effect, and manifests itself to a small degree in temperature fluctuations between day time and night time as well as between warm months and cold months. Hence, the earth as a solar collector functions opposite to conventional above ground solar collectors which rely on direct sunlight for operation, in that the earth reaches its warmest temperatures when heating would be required in buildings and the earth is at its coolest temperature when cooling is required.